This renewal application for the Harvard Medical School Fellowship in Pediatric Gastroenterology and Nutrition combines two T32 awards currently active at Children's and Massachusetts General Hospitals, Boston. The overall goal of the program is to prepare pediatric physician-scientists or non-physician scientists for academic careers in independent research on topics relevant to digestive diseases in infancy, childhood, and adult life. We offer two research training tracks focused on the biology and diseases of the intestine: one in basic or disease-oriented research, and the other in clinical or patient-oriented research. The Disease-Oriented research training track focuses on 1) epithelial cell and developmental biology, 2) innate and acquired mucosal immunology, and 3) epithelial-microbial interactions. The Patient-Oriented research training track focuses on 1) intestinal and nutritional epidemiology, 2) outcomes research, and 3) clinical trials. The program provides an in depth comprehensive scientific experience for each trainee in a research group at the forefront of its field. Ten postdoctoral positions are requested for two years of research training (2 or 3/yr in basic and 2 or 3/yr in clinical research training). Forty outstanding faculty support this effort. Training faculty are drawn from all Harvard Affiliated Hospitals and Research Institutes, the Harvard Medical School, and the Harvard School of Public Health. Opportunities for cross fertilization are abundant. The Program Director is Dr. Wayne I. Lencer, Associate Professor of Pediatrics, Harvard Medical School, a widely respected investigator and mentor. A Career Development Committee is assembled for each trainee to provide mentoring in scientific and career development. Didactic course work is required for both basic and clinical research training tracks and supplemented with relevant seminars and journal clubs, a course in the responsible conduct of research, and a bi-annual research retreat. Trainees in clinical research must obtain a Master's Degree in Medical Science or Public Heath (MMSc or MPH), both from the Harvard School of Public Health. Integration of training with the candidates' future goals in academic medicine, a strong focus on original research, and career development are essential features of the program.